FWIW, I just swapped my stock rear leafs for E-350 dually rear leafs. They bolt right up and have 9 leaves instead of 3 plus overload on my stock leaf pack. E-450 rear leafs are a few inches longer and won't fit.
As far as moto hauling goesm I've now done it 3 ways....all on the rear.
For carrying two motos, I bought a folding Harbor Freight trailer (12" wheel model $240 with a coupon) and modified it rather heavily so that I don't fold the trailer anymore to stand it up...just the tongue. Plywood deck and a few pingle wheel chocks. Light, cheap, folding. If you don't need folding get a non-folding one..they should be more robust.
For carrying a single bike, I've been using my neighbor's Joe hauler. They work great, are a bit heavy when schlepping it onto the hitch though. If you go this way find one with the cam lock anti wobble feature. Older ones screw a bolt into the side of the receiver newer ones have a large hex that you tighten at the very rear of the carrier.
I recently built a custom hitch type hauler with custom dual hitches. The goals were basically to be lighter and less wobbly than a Joe Hauler.
Here's the build thread for that:
http://www.sportsmobileforum.com/for...age-17860.html